1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device which is provided with a movable section to be operated on the basis of a displacement action of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device which is capable of detecting displacement of a movable section by the aid of a piezoelectric/electrostrictive element, and a method for producing the same. In particular, the present invention relates to a piezoelectric/electrostrictive device which is excellent in strength, shock resistance, and moisture resistance and which makes it possible to efficiently operate a movable section to a great extent, and a method for producing the same.
2. Description of the Related Art
Recently, a displacement element, which makes it possible to adjust the optical path length and the position in an order of submicron, is required, for example, in the fields of optical science, magnetic recording, and precision machining. Development is advanced for the displacement element based on the use of the displacement brought about by the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric material).
As shown in FIG. 37, for example, those hitherto disclosed as such a displacement element include a piezoelectric actuator comprising a fixation section 204, a movable section 206, and a beam section 208 for supporting them which are formed in an integrated manner with a hole 202 provided through a plate-shaped member 200 composed of a piezoelectric/electrostrictive material and with an electrode layer 210 provided on the beam section (see, for example, Japanese Laid-Open Patent Publication No. 10-136665).
The piezoelectric actuator is operated such that when a voltage is applied to the electrode layer 210, the beam section 208 extends and contracts in a direction along a line obtained by connecting the fixation section 204 and the movable section 206 in accordance with the inverse piezoelectric effect or the electrostrictive effect. Therefore, the movable section 206 can perform circular arc-shaped displacement or rotational displacement in the plane of the plate-shaped member 200.
On the other hand, Japanese Laid-Open Patent Publication No. 63-64640 discloses a technique in relation to an actuator based on the use of a bimorph. In this technique, electrodes for the bimorph are provided in a divided manner. The divided electrodes are selectively driven, and thus the highly accurate positioning is performed at a high speed. This patent document (especially in FIG. 4) discloses a structure in which, for example, two bimorphs are used in an opposed manner.
However, the piezoelectric actuator described above involves such a problem that the amount of operation of the movable section 206 is small, because the displacement in the direction of extension and contraction of the piezoelectric/electrostrictive material (i.e., in the in-plane direction of the plate-shaped member 200) is transmitted to the movable section 206 as it is.
All of the parts of the piezoelectric actuator are made of the piezoelectric/electrostrictive material which is a fragile material having a relatively heavy weight. Therefore, the following problems arise. That is, the mechanical strength is low, and the piezoelectric actuator is inferior in handling performance, shock resistance, and moisture resistance. Further, the piezoelectric actuator itself is heavy, and its operation tends to be affected by harmful vibrations (for example, residual vibration and noise vibration during high speed operation).
In order to solve the problems described above, it has been suggested that the hole 202 is filled with a filler material having flexibility. However, it is clear that the amount of displacement, which is brought about by the inverse piezoelectric effect or the electrostrictive effect, is decreased even when a filler material is employed.
Further, the actuator described in Japanese Laid-Open Patent Publication No. 63-64640 has such a structure that the bimorph itself is composed of two piezoelectric elements which are laminated with each other, in addition to the fact that the bimorph is stuck to a fixation member or a mediating member. Therefore, the stress tends to remain, resulting from, for example, the curing and the shrinkage of an adhesive and the heating treatment required for the sticking and the lamination. It is feared that the displacement action is disturbed by the internal residual stress, and it is impossible to realize the displacement and the resonance frequency as designed. Especially, when the actuator is small in size, the influence of the adhesive is increased by itself.
Accordingly, a method is conceived in order to exclude the influence of the adhesive required to effect the sticking, in which the actuator is composed of, for example, an integrated sintered product made of ceramics to give a structure in which no adhesive is used. However, also in this case, it is inevitably feared that the internal residual stress arises due to the difference in behavior of thermal shrinkage between respective members during the sintering.
Further, when the actuator is small in size, a problem is involved such that the fixation property of the actuator and the attachment property of the actuator to another part are deteriorated.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a piezoelectric/electrostrictive device and a method for producing the same which make it possible to obtain a displacement element that is scarcely affected by harmful vibration and capable of high speed response with high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance. It is also an object of the present invention to realize a light weight of the device, especially a light weight of a movable section or a fixation section, and improve the handling performance of the device and the attachment performance for parts to be attached to the movable section or the fixation performance of the device, so that the movable section may be greatly displaced at a relatively low voltage. It is a further object of the present invention to achieve a high speed of the displacement action of the device, especially of the movable section (realization of a high resonance frequency), as well as a sensor element which makes it possible to accurately detect vibration of the movable section.
According to the present invention, there is provided a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section; one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section; wherein any one of the movable section and the fixation section has mutually opposing end surfaces.
The movable section, the fixation section, and the thin plate section may be made of ceramics or metal. Alternatively, each of the components may be made of a ceramic material, or each of them may be made of a metal material. Further, each of the components may be constructed to have a hybrid structure obtained by combining those produced from materials of ceramics and metal.
It is also preferable that a cutoff section is provided on any one of the movable sections and the fixation section; and a part of the cutoff section constitutes the mutually opposing end surfaces. It is also preferable that the thin plate section, the movable section, and the fixation section are composed of a ceramic substrate integrated into one unit by simultaneously sintering a ceramic green stack and cutting off unnecessary portions. It is also preferable that the piezoelectric/electrostrictive element has a film-shaped configuration, and it is integrated with the ceramic substrate by means of sintering.
In this arrangement, the piezoelectric/electrostrictive element may have a piezoelectric/electrostrictive layer and a pair of electrodes formed on the piezoelectric/electrostrictive electrostrictive layer. It is also preferable that the piezoelectric/electrostrictive element has a piezoelectric/electrostrictive layer and a pair of electrodes formed on both sides of the piezoelectric/electrostrictive layer, and one electrode of the pair of electrodes is formed on at least the thin plate section. In this arrangement, the vibration caused by the piezoelectric/electrostrictive element can be efficiently transmitted via the thin plate section to the movable section or the fixation section. Thus, it is possible to improve the response performance. Especially, it is preferable that the piezoelectric/electrostrictive electrostrictive element is constructed in a stacked form comprising a plurality of units each including the piezoelectric/electrostrictive layer and a pair of electrodes.
When the arrangement as described above is adopted, the following feature is achieved. That is, the generated force of the piezoelectric/electrostrictive element is increased, and thus it is possible to obtain a large displacement. Further, it is possible to obtain a high resonance frequency owing to the increase in rigidity of the device itself, making it easy to achieve the high speed of the displacement action.
It is also preferable that a gap is formed between the mutually opposing end surfaces. It is also preferable that a member, which is different from a constitutive member of the movable section, is interposed between the mutually opposing end surfaces, the different member including, for example, glass, cement, and organic resin, preferably organic resin such as those based on epoxy, acrylic, polyimide, phenol, silicone, terpene, xylene, styrene, melamine, methacrylic, and rubber, or mixture or copolymer thereof. Especially, in view of, for example, the joining performance, the handling performance, and the hardness, it is preferable to allow organic resin or the like based on epoxy, acrylic, and methacrylic to intervene. In order to further enhance the hardness, it is also preferable to mix a filler such as an inorganic material.
Especially, it is possible to effectively realize a light weight of the movable section or the fixation section by forming the gap between the mutually opposing end surfaces, allowing the member lighter than the constitutive member of the movable section or the fixation section to intervene between the mutually opposing end surfaces, or joining the end surfaces with the member. Accordingly, it is possible to increase the resonance frequency without decreasing the amount of displacement of the movable section or the fixation section. In view of the high resonance frequency, it is preferable that the member is made of a hard material.
When the gap is formed between the mutually opposing end surfaces, a part of the movable section or the fixation section including one end surface and another part of the movable section or the fixation section including the other end surface are more flexible, resulting in strong resistance to the deformation. Therefore, it is possible to obtain excellent handling performance of the piezoelectric/electrostrictive electrostrictive device.
The existence of the mutually opposing end surfaces increases the surface area of the movable section or the fixation section. Therefore, when the movable section has mutually opposing end surfaces, the attachment area can be increased when another part is attached to the movable section. Thus, it is possible to improve the attachment performance for the part. It is now assumed that the part is secured, for example, with an adhesive or the like. In this case, the adhesive is fully distributed to the end surfaces as well as to the first principal surface of the movable section. Therefore, it is possible to dissolve, for example, shortage of application of the adhesive. Thus, it is possible to reliably secure the part.
On the other hand, when the fixation section has mutually opposing end surfaces, it is possible to strongly fix the piezoelectric/electrostrictive device according to this invention to a predetermined fixation portion. Thus, it is possible to improve the reliability.
As described above, according to the present invention, it is possible to obtain the displacement element which is scarcely affected by harmful vibration and capable of high speed response with high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance, making it possible to realize a light weight of the device, especially a light weight of the movable section or the fixation section, and improve the handling performance of the device and the attachment performance for parts to be attached to the movable section or the fixation performance of the device, so that the movable section may be greatly displaced, and it is possible to achieve a high speed of the displacement action of the movable section (realization of a high resonance frequency), as well as the sensor element which makes it possible to accurately detect vibration of the movable section.
In the production of the piezoelectric/electrostrictive device, for example, when the piezoelectric/electrostrictive element is formed on a ceramic stack (obtained by stacking ceramic green sheets followed by sintering into one unit), for example, by means of the lamination or the integrated sintering based on the use of the film formation method as described later on, the internal residual stress is generated at a portion to be formed into the piezoelectric/electrostrictive element and/or the thin plate section. Especially, when the piezoelectric/electrostrictive element is formed on the ceramic stack by means of the integrated sintering, the internal residual stress tends to be generated at the portion to be converted into the piezoelectric/electrostrictive element and/or the thin plate section, due to the shrinkage and the difference in coefficient of thermal expansion of the constitutive members caused during the sintering.
The internal residual stress still remains in the piezoelectric/electrostrictive element and/or the thin plate section even after unnecessary portions of the ceramic stack are cut off to provide the ceramic substrate having the movable section, the fixation section, and the thin plate sections.
If the piezoelectric/electrostrictive device is produced and used starting from this state, the movable section does not exhibit the desired displacement in some cases even when a predetermined electric field is generated in the piezoelectric/electrostrictive layer for constructing the piezoelectric/electrostrictive element, because of the following reason. That is, the material characteristic of the piezoelectric/electrostrictive layer and the displacement action of the movable section are inhibited by the internal residual stress generated in the piezoelectric/electrostrictive element and/or the thin plate section.
In the present invention, the mutually opposing end surfaces are provided on any one of the movable section and the fixation section. Therefore, the distance between the end surfaces is, for example, shortened by the internal residual stress generated in the piezoelectric/electrostrictive element and/or the thin plate section. That is, the internal residual stress, which has been generated in the piezoelectric/electrostrictive element and/or the thin plate section, is released by the movement of the end surfaces.
Therefore, the displacement action of the movable section is not inhibited by the internal residual stress. It is possible to obtain the displacement action of the movable section as approximately designed and expected. Additionally, the release of the stress also makes it possible to improve the mechanical strength of the device.
In the invention described above, it is also preferable that the hole is filled with a gel material. In this arrangement, although the displacement action of the movable section is restricted due to the presence of the filler material, the invention described above intends to reduce the weight as a result of the formation of the end surfaces on the movable section or the fixation section, and increase the displacement amount of the movable section. Therefore, the restriction of the displacement action of the movable section by the filler material is counteracted, and it is possible to realize the effect owing to the presence of the filler material, i.e., the realization of the high resonance frequency and the maintenance of the rigidity.
According to another aspect of the present invention, there is provided a method for producing a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section; one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section; the method comprising a step of forming the movable section or the fixation section having mutually opposing end surfaces by cutting off a predetermined part of any one of a portion to be formed into the movable section or a portion to be formed into the fixation section after producing at least the piezoelectric/electrostrictive element.
As a result, there is provided the movable section and the fixation section which has the mutually opposing end surfaces. Accordingly, the internal residual stress, which has been generated in the piezoelectric/electrostrictive element and/or the thin plate section during the production, is released, for example, by shortening the distance between the end surfaces. Therefore, the displacement action of the movable section is not inhibited by the internal residual stress.
The phrase xe2x80x9cafter producing the piezoelectric/electrostrictive elementxe2x80x9d referred to herein indicates a state in which at least the piezoelectric/electrostrictive layer is formed. As for the electrode to be formed after the formation of the piezoelectric/electrostrictive layer, the electrode may be formed after performing the cutoff to form the movable section or the fixation section having the mutually opposing end surfaces.
The provision of the movable section or the fixation section having mutually opposing end surfaces realizes the light weight of the movable section or the fixation section. Therefore, the piezoelectric/electrostrictive device, which makes it possible to increase the resonance frequency, can be efficiently produced with ease without decreasing the amount of displacement of the movable section. Thus, it is possible to realize the mass production of the high performance piezoelectric/electrostrictive device.
Further, the movable section or the fixation section is bent more flexibly, and it is strongly resistant to deformation. Therefore, the piezoelectric/electrostrictive device is excellent in handling performance. The presence of the mutually opposing end surfaces increases the surface area of the movable section or the fixation section. When another part is attached to the movable section, or when the device is fixed at a predetermined fixation position, it is possible to provide a large attachment area or a large fixation area thereof. Thus, it is possible to improve the attachment performance for the part and the fixation performance of the device.
According to still another aspect of the present invention, there is provided a method for producing a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section; one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section; the method comprising a step of producing a ceramic stack by integrally sintering a ceramic green stack including at least a ceramic green sheet having a window for forming at least the hole thereafter and ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic stack; a step of forming the piezoelectric/electrostrictive element on an outer surface of a portion of the ceramic stack to be formed into the thin plate section; and a cutoff step of forming the movable section or the fixation section having at least mutually opposing end surfaces by means of at least one time of cutoff treatment for the ceramic stack formed with the piezoelectric/electrostrictive element.
Accordingly, in the production of the piezoelectric/electrostrictive device, especially when the piezoelectric/electrostrictive element is formed on the ceramic stack by means of the sintering, the internal residual stress, which is generated in the piezoelectric/electrostrictive element and/or the thin plate section, can be effectively released. Therefore, when the piezoelectric/electrostrictive device is produced by using the ceramic green sheet-stacking method, it is possible to realize a light weight of the device, especially the light weight of the movable section or the fixation section, and improve the handling performance of the device, the attachment performance for parts to be attached to the movable section, and the fixation performance of the device. Thus, it is possible to allow the movable section to make a large displacement.
It is also preferable that in the step of producing the ceramic stack, the ceramic stack is produced by integrally sintering a ceramic green stack including a ceramic green sheet having a window for forming the movable section or the fixation section having at least the mutually opposing end surfaces, and the ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic stack; and in the cutoff step, the movable section or the fixation section having at least the mutually opposing end surfaces is formed by means of the cutoff treatment for the ceramic stack formed with the piezoelectric/electrostrictive element.
It is also preferable that in the step of producing the ceramic stack, the ceramic stack is produced by integrally sintering a ceramic green stack including a ceramic green sheet having a window for forming a portion to be formed into the movable section or a portion to be formed into the fixation section having at least mutually opposing end surfaces partially connected to one another, and the ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic stack; and in the cutoff step, the portion to be formed into the movable section or the portion to be formed into the fixation section having at least the mutually opposing end surfaces partially connected to one another is formed by means of the cutoff treatment for the ceramic stack formed with the piezoelectric/electrostrictive element, and the movable section or the fixation section having the mutually opposing end surfaces is formed by cutting off the connecting portion.
It is also preferable for the production method that in the cutoff step, the hole is simultaneously exposed by means of the cutoff treatment for the ceramic stack. In this process, the formation of the movable section or the fixation section having the mutually opposing end surfaces may be performed simultaneously with the formation of the hole. There is no limitation for the sequence to perform the formation steps.
It is also preferable that the production method further comprises a step of allowing a member different from a constitutive member of the movable section to intervene between the mutually opposing end surfaces.
Therefore, the piezoelectric/electrostrictive device according to the present invention can be utilized as the active device including, for example, various transducers, various actuators, frequency region functional parts (filters), transformers, vibrators, resonators, oscillators, and discriminators for the communication and the power generation, as well as the sensor element for various sensors including, for example, ultrasonic sensors, acceleration sensors, angular velocity sensors, shock sensors, and mass sensors. Especially, the piezoelectric/electrostrictive device according to the present invention can be preferably utilized for various actuators to be used for the mechanism for adjusting the displacement and the positioning and for adjusting the angle for various precision parts such as those of optical instruments and precision mechanical equipments.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.